i have a pioneer head unit and 4 sony 3way 6.5" speekers in the doors. that alone sounds really good. if you are thinking about getting xm, definately do it. (no i do not own any of their stocks nor do i work for them). i absolutely love the service. especially when i get stuck in places like i am now where there are a bunch of radio stations to listen to, as long as you can listen inbetween all the static. god i just love ft leonard wood! stuck in the middle of absolutely nowhere for the next 4 months. god i love it. at least i have access to 100 channels of digital sound, but in reality i only listen to about 20-25 of them. still makes it worth it.
with the poineer units, you really do not need to amplify your door speakers, so you can still use the amp under your rear seat (?) to run a subwoofer. just bridge two of the channels into the sub. you can then mount the xm unit under the driver's seat. or vise versa.
The Almighty 2" BB Jeep Club Member #34 (no more BB)
Silver 98 ZJ 4.0 I-6
K&N FIPK Gen II
JKS Adjustable Track Bars F and R
JKS Adjustable Control Arms
JKS Quicker Disco's
Kevins 3.5" Lift Kit w/ MX-6 Shocks
US Wheel 15x8 10 spoke black Steelies, 31" BFG AT KO rubber